The term vacuum cleaner encompasses a wide variety of appliances that use negative pressure to collect various solids and even liquids into a collection area for disposal. The heart of any vacuum cleaner is the motor/blower unit. This is typically a universal motor with one or more stages of fan blades attached. A typical household unit might be a two horsepower motor with a two stage backward curved fan system. One fan might have six blades and the other seven. On the inlet side of the motor/blower is the bag cavity area. Here, the negative pressure developed by the motor/blower is transferred to the hose and nozzle by the bag volume. There may be one or more filters in addition to the bag to keep dust and large particles from damaging the motor/blower. The outlet of the motor/blower is exhausted to the environment usually through some type of dust filter.
The following patents describe the active noise control system used and are hereby incorporated by reference herein; U.S. Pat. No. 5,091,953 to Tretter, U.S. Pat. No. 5,105,377 to Ziegler, U.S. Pat. No. 4,878,188 to Ziegler and U.S. Pat. No. 4,122,303 to Chaplin et al. This invention incorporates several of the methods and apparatus described to actively cancel noise produced by the vacuum. The multi-channel digital virtual earth system disclosed by the cited references to Tretter and Ziegler are incorporated by reference herein. Ziegler in U.S. Pat. No. 4,878,188, shows a selective active cancellation system for repetitive phenomena which, as stated, is used in duct systems and is "fast adapting" to cancel repetitive and random noise. An improvement of this system is given in Ziegler, U.S. Pat. No. 5,105,377, which allows fast adapting digital virtual earth without a reference signal. The Tretter patent builds on Ziegler, U.S. Pat. No. 5,105,377 and shows the same system with interacting multiple sensors and actuators. Chaplin et al in U.S. Pat. No. 4,122,303, uses two microphones as noise sensor and residual error sensor as described in the specification and disclosure.
Several Japanese patents describing how an active cancellation system is incorporated into a vacuum cleaner are referenced herein; Japanese patent number 5-3841 to Tanaka, Japanese patent number 5-3843 to Iida and Japanese patent number 5-7536 to Saito. The patents by Iida, Tanaka and Saito are limited in effectiveness for canceling broadband noise because the duct is wrapped or bent. This results in poor signal matching between the reference and residual error microphone which results in poor cancellation performance. The reason the duct is wrapped is because of slow processor speeds to avoid feedback from the speaker to the reference microphone and to reduce overall size of the vacuum at the expense of the dust bag capacity. The feedback is not compensated for in the control system.